This invention relates to systems for removing particulate matter suspended in a fluid, and more particularly to systems for removing fine particles from fluid utilized in conjunction with the machining of metal or non-metals.
There are many applications in which it is necessary for environmental reasons, or for the reclamation and recycling of resources, to separate particulate matter suspended in a liquid from the liquid itself. One example of such an application is the need to remove particulate matter from water used by an industrial floor cleaning machine, or a street sweeping machine, prior to disposing of the water in an environmentally safe manner. Another example of such an application is the removal of waste material from coolant used with cut-off saws or grinding machines. Yet another example of such an application is the necessity to separate chips and fine particles of waste material from coolants used with machine tools to facilitate the machining of metal or non-metallic materials.
The process of machining a workpiece into a finished part on a machine tool requires that a cutter of some sort be forced into the workpiece to carve away waste material portions of the workpiece and achieve the desired shape of the finished part. The action of the cutter against the workpiece generates both a large volume of chips or fine particles of waste material, and a substantial amount of heat in the cutter and workpiece. These chips or particles of waste material, and the heat generated, must be transported away from the cutter and workpiece during the machining process, in order to achieve dimensional accuracy of the finished part, and in order to allow the cutter to operate at the high speeds necessary to effectively and efficiently shape the finished part without overheating.
In order to remove the chips or particles, and the heat generated in the machining process, machine tools generally incorporate some sort of cooling and flushing system for directing a flow of a liquid coolant or oil at the workpiece and cutter during the machining process, to absorb the heat generated at the interface of the cutter and the workpiece, and to transport both the heat and chips or particles away from the cutter and workpiece. After flowing over the cutter and workpiece, the coolant fluid, with the chips or particles entrained, is collected and drained from the machine tool.
Modern machining processes are carried out at very high speeds, requiring a large flow of coolant fluid for effective removal of the chips and heat. Depending upon the machining process involved, a continuous flow of coolant is required during the machining process at flow rates in the range of 10 to 400 gallons a minute. This flow of coolant is typically supplied to the machine tool by a coolant fluid circulating and cleaning system which includes mechanisms for separating the chips and particles from the flow of coolant so that the coolant may be continuously re-circulated.
For larger sized chips or particles of waste material, the primary mechanism for separating the waste material from the cooling fluid involves utilizing the force of gravity. In some coolant cleaning systems utilizing scraper type conveyors, the coolant fluid drained from the machine tool is directed into a dirty fluid reservoir of the coolant cleaning system where the chips and particles are allowed to settle in the bottom of the reservoir. A conveyor mechanism then scrapes across the bottom of the reservoir to pick up the settled chips and particles and transports them to a chip collection bin or container. The coolant above the bottom of the tank is then drawn off by a pump and re-circulated to the machine tool. In other coolant cleaning systems, the coolant with entrained chips and particles is directed onto a screen, or a hinge belt conveyor system, as the fluid enters the dirty fluid reservoir, so that the fluid can run through the screen or hinge belt into the bottom of the reservoir, with the larger sized chips and particles being screened out and separated from the coolant fluid by the screen or hinge belt. The cleaned coolant below the screen or belt is then re-circulated to the machine tool. U.S. Pat. No. 5,858,218 to Setlock et al; U.S. Pat. No. 5,849,183 to Ota et al; U.S. Pat. No. 5,603,846 to Uchiyama et al; U.S. Pat. No. 5,167,839 to Widmer II et al; and U.S. Pat. No. 4,992,167 to Uchiyama; are illustrative of these approaches utilizing the force of gravity to separate the chips and particulate matter from the fluid. U.S. Pat. No. 4,895,647 is also illustrative of these approaches, and includes a permanent magnet disposed on the bottom wall of the reservoir to supplement the force of gravity with magnetic attraction of ferrous chips and particles.
Although these coolant cleaning systems utilizing the force of gravity work reasonably well for larger sized chips and particles, there are several inherent problems involved in the practical application of such systems which have led the designers of such systems to also include additional filtration devices in their systems.
For coolant systems relying on the force of gravity to cause the chips and particles of waste material to settle out on the bottom of the dirty fluid reservoir, one inherent problem is that the flow rates of coolant demanded by modern machining processes do not allow the fluid to remain stagnant in the dirty fluid reservoir long enough for smaller chips and fine particles of waste material to settle out in the bottom of the tank. While it would seem at first glance that theoretically all particles of waste material would eventually settle to the bottom of the tank, given enough time, practical considerations such as limitations on floor space prevent system designers from providing dirty fluid reservoirs large enough for this to happen. For example, a coolant system required to provide 400 gallons per minute of coolant to a machine tool would need to have a dirty fluid reservoir capable of holding 2000 gallons of coolant in order to allow the coolant to remain in the reservoir for a period of five minutes before being re-circulated to the machine tool. In practice, a reservoir this large simply takes up too much floor space for most applications, and as a compromise, the dirty fluid reservoir capacity of many coolant cleaning systems is designed to hold only enough coolant for the coolant to remain in the reservoir a minute, or a minute and one half at the most, before being re-circulated. This means that the coolant in the reservoir is never really stagnant, but is actually flowing through the reservoir at a rate high enough to keep some finer particles suspended in the fluid. Swirling and churning of the fluid in the tank, caused by draw down of the circulation pump and the action of conveyors, hinge belts, and the like moving through the reservoir, increase the percentage of finer particles that remain suspended in the coolant.
Even if the coolant in the dirty fluid reservoir could remain relatively stagnant, other factors such as viscosity and surface tension of the coolant would cause a certain percentage of fine particles to remain suspended in the fluid rather than settling out. This is particularly true for finer particle of light metals such as aluminum or magnesium. For the tight tolerances required in some machining operations, even this small percentage of suspended fine particles must be removed by some sort of filtration beyond that provided by the force of gravity.
Coolant cleaning systems that utilize a hinge belt or inlet screen to catch and convey away the chips and particles of waste material as the fluid enters the reservoir, rather than allowing them to settle to the bottom for removal by a conveyor, also must deal with the problem of removing the finer particles suspended in the fluid. All of the factors described above in relation to coolant cleaning systems relying on settlement of waste material in the bottom of the dirty fluid reservoir that cause finer particles to remain suspended in the fluid, such as swirling or churning of the fluid, surface tension effects, etc., are also present in cleaning systems that utilize inlet screens or hinge belts to capture the larger chips and particles as they enter the reservoir and allow the fluid to drain through into the reservoir by the force of gravity. For these systems, as a practical matter, the mesh size of the inlet screen or the spaces that allow passage of the fluid through the belt must be large enough to allow the majority of the waste material to be removed at very high rates, given the large volume of waste material that must be dealt with as a result of the high speeds of modern machining operations. Stated another way, floor space considerations place practical limitations on the size and operating capacities of particulate matter removal and conveying devices, resulting in their being designed to allow the passage of finer suspended particles in order to handle the volume of larger chips and particles in the space available for the inlet screen or conveyor.
In one approach to providing additional filtration of the coolant fluid, U.S. Pat. No. 5,738,782, to Schafer et al, utilizes an edge mounted stationary filter in a partition between a preliminary cleaning area and a clean chamber of a sedimentation chamber, and a scraper type cleaning device mounted on the edge mounted filter for removal of impurities adhering to the filter. It is not likely, however, that the approach taught by Schafer would allow the high coolant volume flow rates required for many modern machining operations.
In the most commonly utilized approach to providing additional filtration of the coolant fluid, a drum filter rotatable about an axis of rotation of the drum is provided. The drum includes a generally cylindrical shaped screen on the outer periphery of the drum. The drum filter is positioned within the dirty fluid reservoir in such a manner that fluid with entrained or suspended particles flows into the drum through the cylindrical screen in a direction of flow oriented generally perpendicular to the axis of rotation of the drum. An opening is provided in an end wall of the drum, and a corresponding opening is provided in a wall of the dirty fluid reservoir, so that once the fluid has flowed into the drum through the cylindrical filter in a direction perpendicular the axis of rotation, the cleaned fluid inside the drum can change direction inside the drum and exit through the opening in the end wall of the drum and the corresponding opening in the wall of the dirty fluid reservoir in a direction generally parallel to the axis of rotation of the drum. A dynamic seal is generally provided in the dirty fluid reservoir between the end wall of the drum and the wall of the dirty fluid reservoir to prevent the dirty fluid from bypassing the drum filter, and to prevent the cleaned fluid exiting the end wall of the drum from re-entering the dirty fluid reservoir. Backwash nozzles for directing a spray of fluid or air either at or outward through the cylindrical screen are also generally provided to remove particulate matter adhering to the outside of the cylindrical screen. Typically the backwash nozzles are located inside the drum. The drum is generally rotated either by a drum sprocket attached to the outer periphery of the drum in such a manner that a portion of a chip conveyor chain or belt moving under or over the outer periphery of the drum engages the sprocket and turns the drum, or by a separate drive apparatus for the drum.
Coolant cleaning systems utilizing drum filters are disclosed in U.S. Pat. No. 5,849,183 to Ota et al; U.S. Pat. No. 5,603,846 to Uchiyama et al; U.S. Pat. No. 5,167,839 to Widmer II et al; U.S. Pat. No. 4,992,167 to Uchiyama; and U.S. Pat. No. 4,895,647 to Uchiyama. Ota et al ""183, and Uchiyama ""167 disclose a filtration apparatus using multiple drum filters in a single filtration apparatus to provide fractional filtration of the dirty coolant so that filtered coolant with varying degrees of cleanliness can be supplied to match the cleanliness requirements of various machining operations.
Although such drum filters have been used for many years in coolant cleaning systems for machine tools, their use is subject to a number of problems, and further improvement is needed. Specifically, drum filters and their associated back washing and support systems are difficult to manufacture and maintain, and inherently subject to damage from the interaction of particulate matter being moved by the conveyor and the circumferential screen on the drum.
Where a drum filter is driven from a drag chain passing below the drum, or runs in close proximity to such a drag chain, as taught by Uchiyama ""647 and ""167, and by Widmer ""839, the waste material being conveyed out of the dirty fluid reservoir by the conveyor must pass under drum in the small space formed by the close proximity between the drum""s cylindrical screen and the bottom of the reservoir. A buildup of chips in this area frequently results in damaging the screen and jamming the conveyor. Clearing such a jam, and replacing a damaged cylindrical screen is not an easy task, due to the shape and location of the parts involved. Clearing a jammed conveyor or filter drum is especially difficult in scraper conveyors in many instances, because the scraper blades are angled with respect to the direction of chain movement in such a manner that makes it difficult to reverse the direction of the chain.
In most drum filter systems, the back washing nozzles are located inside the drum and spray coolant or air radially outward through the cylindrical screen to dislodge any particulate matter adhering to the outside of the screen. Getting fluid plumbing or air supply lines routed into the interior of the drum for connection to the back wash nozzles significantly complicates the design and manufacture of the drum. And if one of the back wash nozzles should become plugged, getting to the affected nozzle to unplug it may require a significant amount of disassembly, reassembly, and associated down time for the coolant system, to complete what should be a relatively simple repair operation.
Prior drum filter systems also typically have had to rely on a dynamic seal located in the dirty fluid reservoir, where the seal is exposed to the abrasive action of chips and particles of waste material floating in or passing through the dirty fluid. Seal life is thus reduced. Furthermore, should they become damaged, replacement of these dynamic seals typically involves a significant amount of disassembly, reassembly, possible removal of the drum, and associated down time for the coolant system, to replace the seal.
In systems where a drag chain or hinge belt passes over the outer periphery of the drum, such as those disclosed in Ota ""183, Uchiyama ""846 and Uchiyama ""647, it may also be necessary to disconnect the chain or hinge belt so that the drum can be removed to replace the screen, unplug the nozzles, or replace the seal, thereby complicating repair procedures even further.
Because a drag chain conveyor or hinge belt conveyor cannot pass through the cylindrical space occupied by the drum, the fluid depth in the dirty fluid reservoir must be greater than it otherwise would have to be if the drum were not there. As a result of this extra depth, such drum filter systems often require a greater depth of coolant, and a taller dirty fluid reservoir profile than would otherwise be required. This extra depth slows the rate at which chips and particles settle to the bottom of the reservoir, because they have a longer vertical path through the viscous and swirling coolant, thereby increasing the length of time for such chips, etc., to cause damage to the seal or the screen while they are suspended in the fluid. Although the extra volume of fluid resulting from this extra depth might seem to provide an advantage in that the settling time between re-circulation is lengthened, the longer settling times required for the fluid to reach the bottom of the reservoir more than negate any advantage that the extra coolant volume might otherwise provide.
In some drum filter applications, such as those taught by Ota ""183, Uchiyama ""846, and Uchiyama ""647, a drag chain wraps around a significant portion of the periphery of the drum and is used to drive the drum about its axis of rotation. In such applications, the side loads imposed by the chain on bearings supporting the drum during even normal operation are large, requiring the bearings and support structures to be more robust than they would otherwise have to be. And to allow for the possibility that the side loads will increase several fold, if the chain or the drum should become jammed, the bearings and support structure must be designed to be much larger than they otherwise would need to be.
It is an object of our invention, therefore, to provide an improved fluid cleaning method and system. Further objects of our invention include providing:
1) an improved filter apparatus and method for removing fine particles from coolant fluid used in machine tool operations;
2) an improved apparatus and method as in 1) above that can be readily retro-fifted into existing coolant fluid cleaning systems;
3) an improved filter apparatus that can be more readily manufactured and/or maintained and repaired than prior filters;
4) an improved filter apparatus that can be utilized to provide fractional cleaning of fluids;
5) an improved coolant fluid cleaning system for providing fractional cleaning of fluids;
6) an improved dynamic seal for rotatable filter assemblies
7) an improved coolant system having a lower profile than prior coolant fluid cleaning systems, thereby allowing the use of a system having a fine filter in machine tools, such as lathes, which have heretofore not been able to utilize prior coolant filtration apparatus;
8) an improved coolant fluid cleaning system requiring less floor space than prior systems; and
9) an improved coolant fluid cleaning system capable of simultaneously removing particulate matter located above, below and in between the upper and lower portions of a chip conveyor belt.
Our invention provides such an improved coolant cleaning method, system, and apparatus, through the use of a filter disk assembly that defines and is rotatable about an axis of rotation of the disk, for removing particulate matter from a fluid flowing through the filter disk assembly in a direction substantially parallel to the axis of rotation of the filter disk assembly.
According to one aspect of our invention, an improved coolant cleaning system includes such a filter disk assembly, connected in fluid communication with an apparatus for circulating a flow of fluid through the filter disk assembly in a direction substantially parallel to the axis of rotation of the filter disk assembly. According to various embodiments of our invention, the filter disk assembly may include a generally planar filter screen having openings for passage of the fluid through the filter screen in a direction substantially parallel to the axis of rotation of the disk assembly. In various embodiments of our invention the apparatus for circulating a flow of fluid may include a dirty fluid reservoir, a conveyor for removing chips and particulate matter from the dirty fluid reservoir, a clean fluid reservoir, with the filter disk assembly providing the sole fluid communication path between the dirty and clean fluid reservoirs, and a fluid supply system having a pump for circulating fluid from the clean fluid reservoir through the disk filter assembly.
According to a second aspect of our invention, a coolant fluid cleaning system according to our invention may include several filter disk assemblies feeding into a single clean fluid reservoir to achieve high volume flow rates of clean fluid. Alternatively, a coolant fluid cleaning assembly according to another aspect of our invention may include several filter disk assemblies, having filter elements of increasingly finer mesh, feeding into several separate clean fluid reservoirs to provide fractionally filtered coolant fluid having varying degrees of cleanliness as required for various machining operations.
According to a third aspect of our invention, an array of back wash nozzles is provided to blast particulate matter clinging to the filter disk assembly back directly onto a hinge belt conveyor in the dirty fluid reservoir so that the conveyor may readily carry the particulate matter blasted loose from the filter disk to a waste material collection bin. Unlike prior coolant fluid cleaning systems wherein such nozzles were inconveniently located inside of a filter drum, however, the back wash nozzles of our invention are completely accessible and serviceable without disturbing either the filter disk or the hinge belt conveyor, so that the nozzles can be conveniently serviced if necessary.
According to another aspect of our invention, an improved two stage dynamic seal is provided for the filter disk assembly, having an elastomeric portion located in the clean fluid reservoir, rather than in the dirty fluid reservoir as in prior drum filter arrangements.
The generally discoidal shape of a filter disk according to our invention allows conveying devices, such as drag chains or hinge belts, to be routed through areas that would have been occupied by the cylindrical screen of the drum filters used in prior coolant fluid cleaning assemblies. This provides a number of advantages. The filter elements in our filter disk assemblies are far better protected inherently from wear, damage, and clogging or jamming than the cylindrical screens used in prior coolant fluid cleaning systems using drum type filters. The filter disk assemblies, dynamic seals, and backwash nozzles according to various aspects and embodiments of our invention can all be readily serviced and even replaced in a matter of a very few minutes without disturbing any conveying devices. Fluid depths in the dirty fluid reservoir can be lower than in prior cleaning systems using drum type filters.
In some embodiments of our invention, the height of the conveying device can also be significantly reduced in a manner allowing a coolant fluid cleaning system, including a filter disk assembly according to our invention for filtering out fine particulate matter, to be utilized with machine tools such as turning centers which have so little room available that it was previously not possible to conveniently provide a system having both a conveyor for particulate matter and a filter for fine particulate matter.
Either a filter disk assembly and/or a dynamic seal according to our invention is readily adaptable to existing coolant fluid cleaning systems that formerly had no fine filtering capability, or were originally equipped with drum type filters. According to one aspect of our invention, an adapter kit is provided to retrofit either the filter disk and/or the dynamic seal of our invention into existing coolant fluid cleaning systems.